Bis-quaternary ammonium salts have been widely used as photosensitive silver halide photographic emulsions (Patent Literature 1, Patent Literature 2, and the like) and as antimicrobial agents and antimicrobial activity enhancing agents to exert antimicrobial activity against bacteria, eumycetes, and the like (Patent Literature 3, Patent Literature 4, and the like).
As for a method for producing a quaternary ammonium salt, for example, (1) a method in which a tertiary amine is reacted with an alkyl halide to generate a halogen salt of a quaternary ammonium and, thereafter, salt exchange with an organic acid salt is performed, so as to produce a desired quaternary ammonium salt (Patent Literature 5), (2) a method in which anion exchange is performed by using a halide salt of quaternary ammonium, phosphonium, imidazolium, or pyridinium and an acid or a salt thereof, so as to produce a desired ionic liquid (Patent Literature 6), and (3) a method in which a trialkyl amine is reacted with a carbonic acid diester to generate a quaternary ammonium alkali carbonate and, thereafter, a reaction with an organic carboxylic acid or phosphoric acid is effected, so as to produce a desired quaternary ammonium salt (Patent Literature 7 and Patent Literature 8) have been studied.
However, these methods have problems in that the number of steps are large and the operations are complicated because the halogen salt or the carbonate is generated as an intermediate and, thereafter, an anion exchange reaction to the desired anion is effected. Furthermore, the methods of the above-described items (1) and (2) have disadvantages that, for example, the halogen salt is formed as the intermediate, this exhibits skin irritation, so as to cause hand roughness of an operator and cause corrosion of instruments, containers, and the like, and has poor biodegradability.
Under such circumstances, a development of a method for efficiently producing a bis-quaternary ammonium salt exhibiting no skin irritation and a low level of metal corrosion behavior has been desired.